Nitrogen and hydrogen combine in the ratio $14:3$ by mass to form an ammonia molecule. Find the formula of the ammonia molecule by calculating the molar ratio. (Given atomic mass of $N = 14 \ u, H = 1 \ u$)

Write the names of the following compounds:
$(a)$ $NiS$
$(b)$ $Mg(NO_3)_2$
$(c)$ $Na_2SO_4$
$(d)$ $Al(NO_3)_3$
$(e)$ $K_3PO_4$
$(f)$ $Ca_3N_2$

Find the ratio by mass of the combining elements in the following compounds. (You may use Appendix $-III$)
$(a)$ $CaCO_{3}$ $(b)$ $MgCl_{2}$
$(c)$ $H_{2}SO_{4}$ $(d)$ $C_{2}H_{5}OH$
$(e)$ $NH_{3}$ $(f)$ $Ca(OH)_{2}$

What is the valency of $(a)$ aluminium in aluminium sulphate,and $(b)$ sodium in sodium sulphate?

Derive the molecular formula for Copper $(II)$ Bromide.

Give the formulae of the compounds formed from the following sets of elements:
$(a)$ Calcium and fluorine
$(b)$ Hydrogen and sulphur
$(c)$ Nitrogen and hydrogen
$(d)$ Carbon and chlorine
$(e)$ Sodium and oxygen
$(f)$ Carbon and oxygen